Loading platforms or ramps have been devised with the goal of compensating for differences in the height of the platform and the truck to be loaded or unloaded. Conventional movable platforms have allowed adjustments such as horizontal extension and vertical elevation of the platform, and have typically been mechanically or hydraulically operated.
In the past, however, movable platforms have not been capable of differential extension of one end of the platform relative to the other, in order to compensate for "non-parallel alignment" of a truck; that is, to cause the platform to move into flush relationship with a side of a truck, where the truck is not parked parallel to the loading dock. In addition, existing platforms have generally required a custom-made dock, or at least one which is substantially modified, with the movable upper surface of the dock pivotally mounted about a horizontal axis. Such platforms include U.S. Pat. Nos. 2,689,965 to Fenton, 3,179,968 to Lambert, 2,993,219 and 3,175,238 to Pennington, and 4,382,307, 4,551,877, 4,727,613, 4,800,604, 4,862,547 as well as German Pat. Nos. 2,321,033, 2,545,707 and 3,305,945 to Alten.
Furthermore, with one exception, none of the existing devices are supported on the top of and slide over said top of an existing loading platform or dock. The German Pat. No. 2,449,797 to Alten appears to disclose a movable device which rests on the top of an existing platform or dock, but which requires a pivotal mounting for the movable extension, thereby precluding the differential extension capability of the present invention.
In addition, none of the previous movable platforms utilizes plural extension cylinders at opposite ends to effect self-compensating differential extension of the platform; nor does any applicable prior art disclose a downturned flange along the outer edge of the platform.
The present invention overcomes a number of inadequacies and disadvantages in prior art loading platforms by providing self-compensation for misalignment of a truck to be loaded, while being relatively simple in construction, with fewer moving and component parts, with an ensuing increase in reliability and decrease in cost to construct and maintain. Further simplicity is achieved by the use of a pneumatic pressure source, which has not been previously considered to be effective in similar applications where it is necessary to synchronize the movement at opposite sides of a large sliding or moving member such as the platform. Importantly, the present invention is accommodated by an existing loading platform or dock without the need for substantial modification thereof, unlike previous platforms which require the entire platform to be pivotally mounted at or near one side and which generally require the use of channels or the like for structural support. Also important is the fact that the present invention minimizes significant safety hazards associated with previous platforms where personnel moving between the dock and the truck are subject to injuries resulting from falling through gaps between the platform and the truck due to misalignment of the truck.